Does a Vertex Shader VAO need a VBO? - ios

Question

I am trying to use a VAO with a vertex shader. This works, but only if I set the length of the bufferData to 0. My understanding is that when using a vertex shader, a VBO is not required because my shader is generating the vertices of a quad. If I attempt to create the VAO without binding a buffer, it will also crash.
As I mentioned, this works, however I am concerned because in Apple's Instruments, the OpenGL Expert reports a severe error:
Draw Call Exceeded Array Buffer Bounds
No Buffer Data - DYFKNoBufferData
Here is the code for generating the VAO:
glGenVertexArrays(1, &vaoID); // Create our Vertex Array Object
glBindVertexArray(avoid); // Bind VAO
GLfloat vertices[12]; // Vertices for our square
vertices[0] = -0.5; vertices[1] = 0.5; vertices[2] = 0.0; // Top left corner
vertices[3] = -0.5; vertices[4] = -0.5; vertices[5] = 0.0; // Bottom left corner
vertices[6] = 0.5; vertices[7] = 0.5; vertices[8] = 0.0; // Top Right corner
vertices[9] = 0.5; vertices[10] = -0.5; vertices[11] = 0.0; // Bottom right corner
glGenBuffers(1, &fboTextureVboID); // Create our Vertex Buffer Object
glBindBuffer(GL_ARRAY_BUFFER, fboTextureVboID); // Bind VBO
// As long as I set the buffer data length to 0
// then my glDrawArrays(GL_TRIANGLE_STRIP, 0, 4) call works
// otherwise I get EXC_BAD_ACCESS
glBufferData(GL_ARRAY_BUFFER, 0, vertices, GL_STATIC_DRAW);
// configure vertex attributes
glEnableVertexAttribArray (...
glVertexAttribPointer(...
...
glEnableVertexAttribArray(0); // Make our Vertex Array Object Inactive
glBindVertexArray(0); // Make our Vertex Buffer Object Inactive
Drawing with:
glUseProgram(vertexShaderProgram);
glBindVertexArray(vaoID);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
Can I safely ignore Apple's errors? I am trying to use a VAO for the vertex shader because I would like to eliminate all the vertex attribute bindings in my drawing code. Or is there a better way to do this with a shader with or without a VAO?
EDIT:
Here is my vertex shader source:
#version 300 es
uniform lowp mat4 uProjectionMatrix;
in lowp vec4 a_position;
in lowp vec2 a_texCoord;
out lowp vec2 v_texCoord;
void main()
{
gl_Position = uProjectionMatrix * a_position;
v_texCoord = a_texCoord;
}
And fragment shader source:
#version 300 es
precision mediump float;
uniform lowp sampler2D uTexture;
in lowp vec2 v_texCoord;
out lowp vec4 fragmentColor;
void main()
{
fragmentColor = texture( uTexture, v_texCoord );
}

Answer 1

You can pick one of two things.
It is perfectly legal to have a VAO that has no attached buffer objects. However, this does not mean "create a buffer object, but don't put anything in it". It means not to attach buffer objects to the VAO. You just call glGenVertexArrays to generate the vertex array, and you're done.
No calls to glEnableVertexAttribArrays. No calls to glVertexAttribPointer. If you're not using vertex arrays at all, you should not be making these calls at all.
It is also perfectly legal to have a VAO that contains buffer objects. These work like normal.
What you can't do is create a buffer object that has no allocation, then try to use it for vertex data. That's what happens if you remove just glBufferData.
So you have to pick one side of the road or the other. Either your VAO uses one or more buffers, or it doesn't. If it uses a buffer, those buffers have to have storage. If it doesn't, then it won't care.